A vehicle is equipped with a transmission for converting driving force of an internal combustion engine installed thereon as a prime mover into a form meeting with traveling conditions so that the same can be taken off according to necessity. As for the transmission, there are known a gear type transmission, a belt type transmission and others. Among them, the gear type transmission is most commonly used because loss of the driving force is small. The gear type transmission has multi-stage speed change gear trains, and by shifting the gear trains such that gears of each stage are meshed with each other, the driving force of the internal combustion engine is converted into a form meeting with traveling conditions and taken off according to necessity.
Such gear transmission can be further classified into, for example, selective slide type, normally meshing type and others, which are classified according to the type for shifting a change gear ratio. The selective slide type has gears mounted on a main shaft connected to an input shaft on the side of an internal combustion engine, on a counter shaft arranged parallel to the main shaft, and on an idler shaft arranged parallel to the main shaft, with the gears on the idler shaft being slid to mesh with the gears on the main shaft and the gears on the counter shaft to transmit the driving force.
Similarly, in the normally meshing type, a pair of gears of those on a required number of speed change stages are normally meshed with each other. It is designed such that gears can be idly rotated in a space between a shaft and the gears. And a pair of gears able to obtain a required change gear ratio are fixed to the shaft by a connecting sleeve on the shaft in order to transmit torque.
Similarly, a known manual type transmission includes a wrong way operation preventing mechanism for preventing the gear from being shifted directly to reverse from the forward maximum speed position (5th speed to 4th speed), a gear squeak preventing mechanism for preventing the gear from generating a squeaking sound when shifted to reverse, and many others. An operation mechanism of such manual type transmission includes a shift and select shaft which is rotated when selecting, and which is moved in the axial direction when shifting, in accordance with the operating state of the shift lever. The operation mechanism has a forward stage low speed (1st-speed and 2nd-speed) shift shaft, a forward stage high speed (3rd-speed and 4th-speed) shift shaft, and a forward stage maximum speed and reverse (5th-speed and reverse) shift shaft. A shift and select lever mounted on the shift and select shaft is selectively actuated.
Furthermore, as a transmission for vehicles, there is one as disclosed in, for example, Japanese Patent Early Laid-open Publication No. 57-137747. The transmission disclosed in this Publication is designed such that a fork shaft of a forward stage is pushed when in reverse shifting, and a counter gear is synchronized with rotation of an output shaft by a synchronous meshing mechanism of a forward stage, thereby to easily obtain synchronism for shifting the gear to reverse and to smoothly shift the gear without generating a gear squeak when in reverse shifting.
In the conventional selective slide type gear transmission, the shift and select lever mounted on the shift and select shaft is swung when in reverse shifting, and a 5th-speed and reverse yoke as a forward stage maximum speed and reverse yoke is slidably moved by the actuation of the shift and select lever. Then the 5th-speed and reverse shift shaft as a forward stage maximum speed and reverse shift shaft is moved in the axial direction to cause a reverse idler arm to be slidably moved, a reverse idler lever being actuated by the movement of the reverse idler arm, a reverse idler gear being brought into meshing contact with a main reverse gear mounted on the main shaft and with a counter reverse gear mounted on the counter shaft by the actuation of the reverse idler lever, thereby to perform the reverse shifting.
However, it has such an inconvenience in that when the reverse idler gear is moved to the main reverse gear side, the reverse idler gear is brought into meshing contact with the main reverse gear and with the counter reverse gear while the main shaft is being rotated, and therefore the gears are not smoothly meshed with each other, thus generating a gear knocking sound (i.e. gear squeak or grinding).
Therefore, a known knocking sound preventing device, in order to eliminate the above-mentioned inconvenience, is provided with a pin and a spring for energizing the pin so that the synchronous meshing mechanism of a forward stage is actuated when in reverse shifting and the main shaft is stopped rotating before the reverse idler gear is meshed with the main reverse gear and with the counter reverse gear in order to prevent generation of the gear knocking sound. Because an operating force for activating the synchronous meshing mechanism has a certain relation with a repulsive force (energizing force) of the spring, it becomes difficult to positively actuate the synchronous meshing mechanism when the speed becomes high at the reverse shift operation, thus resulting in generation of the gear knocking sound.
To overcome the above-mentioned inconvenience, the present invention provides a gear knocking sound preventing device for a transmission which, in a slide selective type gear transmission, is designed such that a forward stage low speed shift shaft is slightly moved in the axial direction in association with the actuation of a shift and select shaft when in reverse shifting. In other words, a forward stage fork and a forward stage shifting sleeve are slightly moved to actuate a forward stage synchronous meshing mechanism, whereby said forward stage synchronous meshing mechanism is positively and surely actuated by means of said forward stage sleeve moved by said forward stage fork, and rotation of the main shaft is stopped before the reverse idler gear is meshed with the main reverse gear irrespective of the speed of the reverse shifting operation, so that said reverse idler gear can be smoothly meshed with said main reverse gear and generation of a gear knocking sound can be prevented.
To achieve the above, in a transmission including a forward stage low speed shift shaft, a forward stage high speed shaft, and a forward stage maximum speed and reverse shift shaft selectively moved in the axial direction or rotated by actuation of a shift and select lever mounted on a shift and select shaft, the present invention provides a gear knocking sound preventing device which is characterized in that it further includes a cam mechanism having a first cam disposed on said shift and select shaft, and a second cam disposed on said forward stage low speed shift shaft so that said second cam can be engaged with and disengaged from said first cam, said first cam being activated in accordance with rotation of said shift and select shaft and being brought into engagement with said second cam when in reverse shifting so that said forward stage low speed shift shaft is slightly moved in the axial direction to activate a forward stage synchronous meshing mechanism.
According to the construction of the invention as briefly described above, when the shift and select shaft is rotated to perform a reverse shifting, the first cam is pivoted to engage with the second cam, the forward stage low speed shift shaft is slightly moved in the axial direction through the second cam, the forward stage synchronous meshing mechanism is actuated by the axial movement of the forward stage low speed shift shaft through the forward stage fork and the forward stage shifting sleeve, and the rotation of the main shaft is stopped before the reverse idler gear is meshed with the main reverse gear. As a result, even if the speed of a reverse shifting operation becomes high, the forward stage synchronous meshing mechanism is surely actuated and the reverse idler gear is smoothly meshed with the main reverse gear, thus enabling the gear knocking sound to be avoided.